Rubber compositions for tires capable of roughening the tread surface of a tire and increasing the affinity with ice have been developed conventionally with the objective of improving the on-ice friction of a studless winter tire.
For example, International Patent Publication No. WO/2012/144605 describes “a rubber composition for a tire comprising: 100 parts by mass of a diene rubber (A); from 30 to 100 parts by mass of carbon black and/or a white filler (B); from 0.3 to 30 parts by mass of a crosslinkable oligomer or polymer (C) which is incompatible with the diene rubber (A); and from 0.1 to 12 parts by mass of three-dimensionally crosslinked microparticles (D) having an average particle size of from 1 to 200 μm” ([claim 1]). In addition, Japanese Unexamined Patent Application Publication No. 2013-010967A describes “a rubber composition for a studless winter tire comprising: 100 parts by mass of a diene rubber (A); from 30 to 100 parts by mass of carbon black and/or a white filler (B); from 0.3 to 30 parts by mass of a crosslinkable oligomer or polymer (C) which is incompatible with the diene rubber (A); and from 0.1 to 12 parts by mass of three-dimensionally crosslinked microparticles having an average particle size of from 1 to 200 μm” ([claim 1]).
However, when the present inventors conducted extensive research on the rubber compositions for tires described in International Patent Publication No. WO/2012/144605 and Japanese Unexamined Patent Application Publication No. 2013-010967A, it became clear that there is room for improvement in the on-ice performance and wear resistance.